Spring Boot Built-in API Versioning

Spring Boot 4 introduces built-in API versioning support via the `spring.mvc.apiversion.*` configuration properties. Two versioning strategies are covered: HTTP header-based and request path-based. The tutorial walks through defining versioned REST controllers using the `version` field in mapping annotations (e.g., `@PostMapping(version = "v1.2")`), supporting version ranges like `v1.0+`. Client-side versioning is also supported via `RestClient`, `WebClient`, and `RestTestClient` with `ApiVersionInserter`. Integration with Springdoc OpenAPI 3.0.0 for grouped API docs is attempted but currently has issues. Full code examples and curl test commands are provided.